function AjaxRequest() {
        Ajax = false;
        if (window.XMLHttpRequest) { // Mozilla, Safari,...
            Ajax = new XMLHttpRequest();
        } else if (window.ActiveXObject) { // IE
            try {
                Ajax = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
                try {
                    Ajax = new ActiveXObject("Microsoft.XMLHTTP");
                } catch (e) {}
            }
        }
   }
   function retornapagina(pagina){
      var conteudo = document.getElementById('conteudo');
      AjaxRequest();
      if(!Ajax){
      conteudo.innerHTML = 'Erro na chamada';
      return;
      }else{
      conteudo.innerHTML = '<br><br><p align=center><img src="znload.gif"></p><br><br>';
      }
      Ajax.onreadystatechange = mudapagina;
      Ajax.open('GET', pagina, true);
      Ajax.setRequestHeader("Content-Type", "text/html; charset=iso-8859-1");
      Ajax.send(null);
   }
   function mudapagina(){
      var conteudo = document.getElementById('conteudo');
      if (Ajax.readyState == 4) {         
         if(Ajax.status == 200) {
            conteudo.innerHTML = unescape(Ajax.responseText);
         } else {
            conteudo.innerHTML = 'Erro na requisição da página.';
         }
      }
   }